tests: only run test 50 on x86_64
tests: only run test 50 on x86_64

Because of the way libseccomp handles non-native arch translations we
can't use arbitrary syscalls, e.g. 1000; we need to use syscalls that
are defined in the libseccomp syscall tables.  Unfortunately, changing
the syscalls from 1000/1001 to a defined syscall appears to break the
test so let's just limit it to x86_64 for now.

Signed-off-by: Paul Moore <a027184a55211cd23e3f3094f1fdc728df5e0500@paul-moore.com>

seccomp/libseccomp,seccomp/libseccomp,seccomp/libseccomp